(define (eval exp env)
  (cond ((self-evaluating? exp) exp)
        ((quote? exp) (text-of-quotation exp))
        ((assignment? exp) (eval-assignment exp env))
        ((definition? exp) (eval-definition exp env))
        ((if? exp) (eval-if exp env))
        ((let? expr) (evaln (let->combination expr) env))
        ((lambda? exp)
         (make-procedure (lambda-parameters exp)
                         (lambda-body exp)
                         env))
        ((begin? exp)
         (eval-sequence (begin-actions exp) env))
        ((cond? exp) (eval (cond-if exp) env))
        ((application? exp)
         (apply (eval (operator exp) env)
                (list-of-values (operands exp) env)))
        (else
          (error "Unknown expression type -- EVAL" exp))))

(define (let? expr) (tagged-list? expr 'let)) 

(define (let-vars expr) (map car (cadr expr))) 

(define (let-inits expr) (map cadr (cadr expr))) 

(define (let-body expr) (cddr expr)) 

(define (let->combination expr) 
  (cons (make-lambda (let-vars expr) (let-body expr)) 
        (let-inits expr))) 
